. >> reporter: so far, no one has claimed responsibility, but suspicion falls on the same pakistan-based group that attacked mumbai in 2008. this time, mumbai was better prepared, but the violence would inflame tension between two old enemies, india and pakistan, both nuclear powers. richard engel, nbc news, cairo. >>> and here in our new york studios our chief foreign affairs correspondent andrea mitchell. this is your line of work, you ask any u.s. official what keeps you up at night, and they answer, these two countries, nuclear nations and especiallily pakistan. >> pakistan is about to pass france as the fifth greatest nuclear power in the world and they're on a hair trigger. there's no hot line between india and pakistan, only last week, diplomats from both countries meeting out at stanford university trying to talk about establishing a hotline. so unlike the cold war, there is no communication, they could have an accident. this time india has said in the past that they were restrained three years ago when it was proved that pakistan was behind the attack, they were restrained by the u.s.